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EPRI Assessment of PISCES Water Characterization Studies Introduction The US EPA recently announced its intentions to conduct a two-year study to determine whether the Steam Electric Categorical Effluent Guidelines should be revised. An element of EPA's two-year study will involve data collection at various sites to provide data on waste streams from power utilities. To informthe EPA inits Effluent Guidelines Study, the Electric Power Research Institute (EPRI) is providing the results from its earlier research studies characterizing power plantwastewater streams at seven sites. Much ofEPRI's research efforts were conducted in the late 1990s and early 2000s and often for varying objectives, some of which were site-specific needs. Thus EPRI believes itis critical to provide our perspectives on the results ofthese studies. The following documentis an evaluation of the wastewater data obtained during the PISCES wastewater field studies. The evaluationincludes a critical assessment ofthe data quality and collection techniques for liquid samples in the PISCES data setcollected in the late 1990s and early 2000s as compared to data quality and collection techniques for samples collected by today's sampling and analytical protocols. This evaluationreflects how representative the data setis ofSteamElectric Utility industry as a whole, andhow representative the PISCES data from the late 1990s are compared to plantoperating conditions atthose facilities today, and includes key lessons learned in attempting to characterize power plantwaste streams accurately. 

## PISCES Overview In 1988, EPRI initiated the Power PlantIntegrated System-Chemical Emissions Study (PISCES) project to characterize the distribution oftrace substances in air and liquid streams from fossil-fuel-fired electric utility power plants. The initial focus ofthis effort was on flue gas (air) emissions, in response to the Clean Air Act Amendments. Atthe completion of this effort, EPRI shifted its focus to expand the level ofknowledge oftrace substance concentrations ininternal and effluentwaste water streams infossil-fuel power plants. EPRI along with various hostutilities co-sponsored sampling studies ofwastewater streams at seven power plants during the late 1990s and early 2000s. To maintain consistent sampling and analytical protocols throughout the research project, EPRI selected CH2M HILL to conductthese field studies. The methods ofcollection and analyses utilized were chosen in an effort to minimize contamination and enhance analytical sensitivity while maintaining accuracy and precision. Investigators characterized ash sluice wastes, flue gas desulfurization (FGD) scrubber wastes, plant sump discharges, cooling tower blowdown, coal pile runoff, water treatmentresiduals, and plantintake water at seven stations. 

## Key PISCES Characterization Observations and Lessons Learned The PISCES characterization studies were oflimited scope (only 7facilities) and duration. Therefore, conclusions based on the studies maynotbe generally applicable to the rest of

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the industry. However, this section summarizes the key lessons learned during the PISCES studies:

• Ash ponds are generally effective inremovingTSS andparticulate-bound metals. Removal of dissolved trace metals is more complex and site-specific.

• Ash pond pH appears to be related to the calcium and sulfate concentration in the fly ash.

• Fly ash sluicingis a major source ofmetals to the ash pond.

• Coal properties and boiler types affectfly ash characteristics and constituents.

• Clean methods provide more reliable characterization of the ash pond effluent and other streams with trace metallevels.

• Daily variability ofthe NPDES and ashpond effluent appears to be relatively minor due to the residence times and mixing associated in the ashpond (will notlikely change daily, butwill change on a weekly or monthlybasis).

• Seasonal variability canbe significant and is often related to coal properties and other plant operational changes (e.g., operation of an SCR/SNCR), in addition to natural weather effects such as rainfall.

• Samplingmethods for difficult streams were developed, such as fly ash sluice water. This will be summarized in more detail in a separate EPRI document "Sampling & Analytical Plan Guidance for Water Characterization ofCoal-Fired SteamElectric Utility Facilities" to be provided to EPA. 

## Do the Data from the PISCES Studies Represent the Sites Today? For the PISCES wastewater characterization studies, EPRI partnered with various host utilities who voluntarily participated and provided substantial financial supportto conduct these detailed measurements. Because ofthis, the hostutility generally had specific objectives to address. In addition, due to the uniqueness ofeach power plant design and wastewater managementapproach, each site testplanwas developed in close coordination with the hostutility. To help encourage participation in these wastewater characterization studies, EPRI agreed to notidentify the name ofthe utility and the power plant. A description ofthe field studies at the 7 power plants is provided inTable 1.



### 2 3/9/2007Table 1. Summary Description of EPRI PISCES Water Characterization Sites

Ash Recent Known Site Coal Boiler FGD SCR Handling Comments Plant Changes Added SCRs, Periodically wet SNCR, and FGD. A E. Bit. Tangential N N Dry ash handles Different coal. Added SCR. Planned FGD (2010). Units 1-4 to be replaced with new unit. Unit 5 Focus on now sells most of impacts of its fly ash, and now specific coal functions similar to B E. Bit. Tangential N N Wet sources drv ash handling. Added SCR and Focus on FGD. Different impacts of coal. 803 injection specific coal no longer 

## c E. Bit. Wall N N Wet sources employed Added SCR, Venturi upgraded existing scrubber; once- FGD, added pH through water control to waste 0 E. Bit. Tangential y N Wet management water Zero surface water discharge with pond recycle to Added SCRs and E E. Bit. Wall y N Wet cooling lake additional FGDs. Venturi Added SCRs and scrubber; once- additional new through water generation onceF E. Bit. Cyclone y N Wet management through FGD
E. Bit+ Focus on G W. Sub Cyclone N N Wet ammonia Added SCR

3 3/9/2007Some sites chose to participate in the PISCES program to address specific wastewater issues. Below is a summary ofeach site's objectives which may affect the uniqueness of the site:

• Sites A and Bare summarized inPISCES Water Characterization FieldStudy: SitesA andB (TR-108890, Volumes 1 and 2). Site A employed dry ashhandling. However, the dry ash handling systemperiodically experienced operational issues, at which time the ash was wet sluiced. Selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), as well as wetFGDs hasbeeninstalled atthe various units. The coal supply at Site A has changed, and a different coal is nowbeingburned. For Site B, the coal/fly ash tended to yield high arsenic and selenium concentrations in the ash pond, and thus these concentrations are likely to be in the high end of the range for the overall industry. The coal supply at Site Bhas changed, and a different coal is now being burned. An SCR has now been installed atSite B, and plans havebeen made to shut down Units 1-4 and to repower with a new unit. Site BUnit5 now sells most ofits fly ash, and now functions similar to dry ash handlingfacility.

• Site Cis summarizedin

### PISCES Water Characterization Field Study: Site C 

### (TR-108891, Volumes 1 and 2). AtSite C, studies were performed to assess the relationship between acidic coal, cationic metals, and ash pond performance. At the time of the studies, this site employed S03 fly ash conditioningwhich acidified the fly ash sluice water. This site currently does notburn this acidic coal, and S03injection is no longerutilized. SCR and wetFGD have beeninstalled atthe site.

• Site Dis summarizedinPISCES Water Characterization FieldStudy: Site D (TR108892, Volumes 1 and 2). Two units employedFGDs with combinedparticulatejS02 capture as well as a once-through water management system; the data are oflimited use for characterizingrecycled water management or newer wet FGDs. SCR and an upgraded FGD systemhave nowbeeninstalled atthe site, as has added ash pond pH control system.

• Site E is summarized inPISCES Water Characterization FieldStudy: Site E (TR-112433, Volumes 1 and 2). This site does nothave an NPDES regulated discharge nor an NPDES permit. Recycling ofthe ash pond and otherwaters into a cooling lake is employed at the site. Additional FGDs as well as SCRs have also been installed atthe site.

• Site F is summarized in PISCES Water Characterization FieldStudy: Site F (TR114966). In this study, aqueous ammonia was directly added to the ash pond to simulate ammoniaflue gas slip from the SCR, so data are notrepresentative of actual operating conditions. Two units employed FGDs with combined particulatejS02 capture as well as a once-through water management system; the data are oflimiteduse for characterizing recycled water management ornewer wet FGDs. The FGD pond discharged to the ash pond, so the ash pond water was affected by addition ofdissolved constituents of FGD wastewater. FGD wateruse was higher than more modern FGDs, so constituents may be less concentrated. SCRs and a third FGD havebeeninstalled at the site.

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• Site G is summarized inPISCES Water Characterization FieldStudy: Site G (1001404). The focus of this study was ammonia in the ash pond, so much less metals data were collected. Similar to Site F, aqueous ammonia was directly added to the ash pond to simulate ammonia flue gas slip from the SCR, so data are not representative of actual operating conditions. SCRs have been installed atthe site. 

## Do the PISCES Sites Represent the Current Steam Electric Industry? A goal ofthe PISCES programwas to characterize wastewater streams from across the utility industry. The PISCES programincluded only seven sites. This compares to about 500 coal-fired power plants in the U.S. Using a small sub-set

**(~1** 

### %) has inherentlimitations on the representativeness ofthe industry as a whole. Further, these sites were volunteers and several chose to participate because ofunique needs atthe site. Further, because objectives varied by site, the data collected differed between sites.
Inevaluating whether the PISCES sites representthe industry as a whole, itis useful to understand whatfactors may affectwastewater. The major factors thatmay influence a station's liquid and solid waste streams include:
• Fuel characteristics: Variation incoal characteristics when eitherbottomoffly ash is wet sluiced can affect wastewaterpH and metals contentin ashponds. Dry stack facilities' runoffwould also be influenced by coal properties buthandlingis different and discharge quantities generally lower than those from sluicing ponds. The origin of the coal as well as whether the coal is washed mayinfluence the constituents seen in wastewater effluent and other internal water streams.

• Ashhandling system: Wet sluicing offly ash will resultin increased introduction of metals and other constituents to ashpondwater compared to sites that use dry fly ash handling.

• Air emission control technologies can affect wastewater: Flue gas desulfurization (FGD) scrubbers capturevolatile metals along with acid gases. FGDs can also add a significant suspended solids load, depending on the FGD's liquid-solid separation process. FGD design and operations, such as using lime or limestone, age, recycled or once-through scrubber design, oxidation approach, scrubber additives, make-up water source and management, and coal chloride concentrations, are otherfactors which affect FGD performance and, therefore, wastewater loads.

- Particulate matter (PM) control devices such as cold-side electrostatic precipitators (ESPs), hot-side ESPs, and fabric filters canimpact wastewaterifthese discharges are wethandled as these devices capture fly ashwhich contains trace metals. Ammonia slip from Selective Catalytic Reduction (SCR) or Selective Non-Catalytic Reduction (SNCR) can enter the plantwastewater iffly ash is wet sluiced and ifslip is significant. However, data from newly installed plants indicate thatmany operate with little or no slip.



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• Geographical location: The geographic location impacts the availability ofnearby water sources, impacts the amount ofwater used and therefore the amount of water discharged as effluent. Geographic location also affects the potential coals that may be burned and quality of source water which has the potential to impact wastewater. Wastewater treatmenttechnology: Many coal-fired plants use ashponds, which are primarily designedfor ash disposal, butwhich also provide some treatment. Some facilities use constructed, tank-based treatmentfor some or all wastewater streams. Water supply quality: A plant's source water canhave a significant impact on some parameters, especially when considering the lowlevels presentin ashpond discharges.

• Cooling towers and condensers: The presence ofcooling towers aids inmitigating thermal increases butmay contribute trace metals from the cooling tower materials. The metallurgy ofthe condenser will also impactthe trace metal contribution.

• Boiler type: Within coal-fired power plants, the type ofboiler will influence the wastewater characteristics in that different amounts ofwater will be needed to sluice bottom or fly ash. Pulverized coal plants generate a split of approximately 75% fly ash and 25% bottom ash, while cyclone boilers will generate a split of25% fly ash and 75% bottom ash. In addition, pulverized coal and cyclone boilers will produce differing fly ash characteristics. Bottom ash also tends to be heavier and more chemically inert than fly ash. Ourreview ofthe available data and comparisonwith the overall industry identified the following gaps and analytical needs: Mostofthe PISCES field study sites were located inthe southern US; however, other facilities are located in this as well as other regions of the country. The focus ofthe studies was with fly ash ponds, and thus sites thatwet sluiced fly ash. Only one site employed dry ashhandling. Power plants burningwestern, sub-bituminous, and lignite coals are not represented in this study. The PISCES field studies were conducted in the late 1990s, and atthattime, few power plants employed SCR/SNCRs and only a fraction employed wet FGDs. With the CAIR and CAMR air regulations, many power plants are now installing SCRs as well as new "state-ofthe-art" FGDs. New FGDs, and specifically FGDs which employ limestone as the reagent anduse forced oxidation to produce a gypsumproduct are notrepresented inthe PISCES studies. Sites usingfuels other than coal were notincluded. There are several thousand steam electric utility sites firing other fuels such as oil, natural gas, or refuse-derived fuel, as well as nuclear generatingunits. The PISCES studies were conducted approximately 10 years ago, employingthe "state-ofthe-art'' sampling and analytical methods -atthattime. Analytical methodshave evolved; particularly for Se and As speciation. There is a better understanding ofthe complexities of sampling and analysis for Se and As speciation. For Se there is a trend toward using hyphenated methods (IC-ICP/MS) and away from hydride generation (EPA 1632). These

6 3/9/2007analytical methods require further evaluation and the appropriate method(s) should then be applied to obtain a consistent, high-quality database. 

## Sampling and Analytical Methods: Lessons Learned The 7 PISCES field studies provide many useful insights in conductingfuture sampling and analytical studies. Detail guidance is beingprovided to EPA in a separatereport "Sampling and Analytical Plan Guidancefor Water Characterization ofCoal-Fired Steam Electric Utility Facilities". This section provides a brief summary of some of the key issues:

• Analytical procedures including arsenic and selenium speciation methods • Cleanversus conventional samplingmethods • Solids digestion • Laboratory contaminationfrom glassware (boron contamination) 

### Analytical Procedures including Arsenic and Selenium Speciation The methods utilized during the PISCES programin the 1990s included some ofthe newest "cuttingedge" methods under developmentby the EPA and specifically selected analytical laboratories. These were the "1600 series" methods which complemented traditional methods of analyses from EPA SW-846, such as method 6010 (Inductively Coupled Plasma Emission Spectroscopy

- ICPES), and the 7000-series methodsfor Graphite Furnace Atomic Absorption Spectroscopy (GFAAS). Sample preparationfor the ICPES and GFAAS (SW846, 6010B and 7000 series) methods were takenfrom the SW-846 3000-series methods (digestion techniques) which were determinedbased on the matrix. These digestion methods and the analytical method have notchanged significantly since the 1990s. Each ofthe 1600-series methods includes self-contained preparation techniques within the procedures section. From the 1990s to present, these.methods have notchanged significantly; many ofthe methods were then, and are currently, appendedby the letter "M" to suggestaslightintralaboratory (which was also often interlaboratory) slight modification to the DRAFT 1600 series methods. All ofthese methods were "performance-based". The methods used during the PISCES studyinclude:

• EPA 1631(M)- Mercury (and Methyl-Mercury) byCold Vapor Atomic Fluorescence Spectroscopy • EPA Method 1632(M)

- Determination of Arsenic and SeleniumSpeciation by Hydride Generation • EPA Method 1638(M)

- Determination of Elements by Inductively Coupled Plasma Mass Spectrometry These 1600-series methods are still utilized by laboratories and many are still appended by the "M", as modified. All analytical methods are influencedby the matrix which is prepared and analyzed.



### 7 3/9/2007The arsenic and selenium speciation method usedin the PISCES studies (EPA 1632(M)), is an operationally-defined method thatis still used for arsenic and selenium speciation. The method has notbeenmodified since the late 1990s when the PISCES data were collected. Potential matrix interferences may bias a measurementhigh or low depending on the type ofmatrix interference. Certainwater streams such as those withhigh suspended solids may cause such matrix interferences. Recently, laboratories that specialize inmetal speciation analysis have adopted analytical techniques (notlimited to metals) which place different instrumental techniques in series to obtainbetter specificity for metal species and to reduce interferences and/or enhance detectionlimits. The combination ofion exchange chromatography or high pressure liquid chromatography with inductively coupledplasma mass spectrometry (IC-ICP-MS or HPLCICP-MS) allows the analyst to quantify complex arsenic and selenium species that may have an impact onarsenic and seleniumfate inpowerplanttreatment systems. Some of the seleniumforms identified inutility wastewaters using these methods include selenocyanate, methylseleninic acid, and various unidentified seleniumcompounds. 

### Clean versus Conventional Sampling and Analytical Methods Two distinct sampling and analytical methods were used for samplingin the PISCES study: clean and conventional. Clean sampling and analytical methods for metals were used, and are recommended, atlocations where concentrations ofmetals were expected to be near or below detection limits ofconventional methods. Conventional methods were used for streams withhigher levels ofmetals. Cleanmethodologies refer only to trace metals samplingand analysis. Cleanmethods consisted ofthe EPA Method 1669 "clean" samplingprotocols and 1600- series low-level analytical techniques. Locations using clean methods included the plant intake, cooling water, source water, and ash pond water. The conventional analytical methods (due to their lack of sensitivity atlow levels) were found to more frequently have results considered potentially false positives (Type I, alpha errors) because they were measured at or near the method detection limit. For example, ash pond water collected using cleanmethods reported 0.07 J.Lg/L of cadmium (reportinglimit of0.011 J.lg/L), while using the conventional method in a side-by-side collection reported 0.5 J.lg/L with a reporting limit of0.18 J.lg/L. Itis suspected that the clean result is more accurate because the conventional resultis near its detection limit. The conventional method also had more contamination of samples for more commonly seen metals such as copper and zinc. Analysis of data collected in the PISCES studies, inwhich state ofthe art "clean" sampling and analytical techniques were used, indicated thathistorical data for ash pond mercury, copper, and zinc were likely biased high as is showninFigure 1. This bias was probably due to contamination or method inaccuracy. Table 2 includes a summary ofreporting limits for trace metals based onboth the clean and conventional methods. The reporting limits for clean methods are generally muchlower than that ofconventional analytical methods, so data canbe obtained atlower levels.



### 8 3/9/2007Hg (ng/L)

# r-**~** - Historical literature data**~--** ---- Cu (ug/L) :**~·--·~a····~** D -PISCES Field Studies, conventional
0 -PISCES Field Studies, clean 

# +- Zn (ug/L) 1

_L_J_!__i-'-lJ+---

_ -· Li__Ll_C

__ __J__J_**~** _ "------L_L

_**~'"-'---** 1'0 100 1,000 10,000 5th to 95th Percentile Range of Effluent Concentrations

Figure 1 Difference Between Historic Literature and PISCES Field Studies Data



### Solids Digestion The analytical and preparation method inearly rounds ofthe PISCES program (SW-846 digestion method 3050A) used during ash analysis resulted in incomplete digestion of ash, which provided low-biased results for several parameters. A modified methodfor ash digestion was subsequently performed (ASTM D 3682) and is recommended for future ash analyses.



### 9 31912007Table 2. Reporting Limit Ranges for Clean and Conventional Methods for Trace Metal Analyses in Ash Pond Effluent Parameter Conventional Method Clean Method Range of

**Re~orting** Limits Range of

**Re~orting** Limits {gg[!J 

### L!!91Y Antimony 1.0-21 0.001-0.03 Arsenic 0.88-125 0.018-2.0 Beryllium 0.088-1.0 0.002-0.149 Cadmium 0.1-2.8 0.002-0.08 Chromium 0.45-8.4 0.0102-0.54

Copper 0.84-10.0 0.005-0.16

Lead 1-43.6 0.0073-0.69 Mercury 0.082-0.2 0.000024-0.2 Molybdenum 10-20 0.002-0.0449 Nickel 1.0-6.4 0.0044-0.055 Selenium 1.0-650 0.0059-1.8

Silver 0.31-10 0.002-0.063 Thallium 0.002-19 0.00075-0.01 Vanadium 0.39-10 0.015-0.33 Zinc 0.62-10 0.0054-1.02 

### Laboratory Contamination from Glassware (Boron Contamination) Questions were raised after the PISCES program about whether boronleaching from laboratory glassware (borosilicate) mayhave biased the wastewater characterizationhigh. Blanks were found to contain up to 294 r.tg/L ofboron. Approximately 25% ofthe blanks collected actually resulted inboron detections. In evaluatingPISCES data, results less than five times the maximumblankcontamination are considered questionable due to possible blank contamination. The median ashpond effluent data was below five times the maximumblank detection, whichmay indicate some blank contamination. Ash pond effluentwater had levels ofboronwith a median ofroughly twice the maximumblank contamination. Therefore, the ashpond samples may be biased high. Fly ash sluice water and FGD wastewater typically hadboronconcentrations well above thatfound inblanks, butmay also be somewhataffected by the potentialfor boroncontamination. Based on the re-analyses ofthe PISCES data, future work should instruct the laboratory to avoid the use ofborosilicate glassware during analyses ofwater samples for low levels of boron.



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